Bowden, the gang's distributor and ammunition quartermaster, supplied the three with a Colt Python revolver loaded with .357 Magnum Semiwadcutter bullets.

The following day – June 26, 1996 – while driving her red Opel Calibra, Veronica Guerin stopped at a red traffic light on the Naas Dual Carriageway near Newlands Cross, unaware she was being followed; she was shot six times, fatally, by one of two men sitting on a motorcycle.

As a member of the Sunday Independent staff, Veronica specialised in crime stories.

She soon made a name for herself for hard-hitting pieces that sought to expose the truth about Dublin's burgeoning drug trade and the part that increasingly violent and ruthless organised gangs played in it.

She was outraged by the mob activity she documented and frustrated by the inability of the police to bring the crime bosses to justice, so she launched a virtual one-woman crusade to bring down the gangs.

Veronica's investigative style was a combination of tenacity and boldness.

She typically worked out of her car rather than an office, staying on a story for weeks and weeks – long after many other reporters would have given up.

Sometimes she even camped out on a person's doorstep for days until he would agree to talk to her. And she didn't rely strictly on police sources for her information.

Instead, she went directly to the criminals themselves, persuading many of them to talk to her and detail their activities.

In October 1994, Veronica experienced the first serious repercussions from one of her stories when two bullets were fired through the window of her home as she played with her young son.

Just a couple of months later, in January 1995, she opened the door to her home and came face-to-face with a man who pointed a handgun at her head, then lowered it and shot her in the thigh instead. The man fled, and was never identified.

After leaving the hospital, Veronica, still on crutches, had her husband, Graham Turley, take her to see every crime boss she knew – "just to let them know I wasn't intimidated" – she later revealed in an interview.

In September 1995, Veronica paid a visit to a horse farm owned by a prominent ex-convict, John Gilligan, a known leader in the Dublin criminal underworld.

She questioned him about how he was able to afford such a luxurious lifestyle with no apparent income.

He responded by ripping open her shirt to look for hidden microphones, and then beating her. During a subsequent telephone conversation, he threatened to rape her son and kill her if she published anything about him in the newspaper.

Gardai immediately suspected that Gilligan's gang was responsible for her murder.

Veronica's funeral was attended by the then Taoiseach, John Bruton, who described her murder as an "attack on democracy".

Trade unions called for a moment of silence in her memory, which was observed by people around the country in what was a hugely emotional time which quickly turned to outrage.

Within a week of her murder, the government enacted new laws which led to the establishment of the Criminal Assets Bureau and allowed assets purchased with money obtained through crime to be seized.

After the murder, Bowden agreed to turn State's witness and become the first person to enter the country's witness protection programme.

Granted immunity from prosecution, he was the only witness to give evidence against all four drug gang members at their trials in the Special Criminal Court: Patrick Holland, Paul 'Hippo' Ward, Brian Meehan – and John Gilligan.

In 1997 while acting as a Garda witness, Bowden named Patrick 'Dutchy' Holland in court as the man who supplied the gun.

In November 1998, after evidence from Bowden and others, Ward was convicted of the murder and sentenced to life in prison as an accomplice, because he had disposed of the murder weapon and the motorbike.

This conviction was later overturned on appeal.

Brian Meehan fled to Amsterdam with John Traynor, but was later convicted of the murder and sentenced to life imprisonment.

Gilligan left the country the day before Veronica was murdered, on a flight to Amsterdam.

He was arrested 12 months later in the UK trying to board a flight for Amsterdam, after a routine search of his baggage revealed $500,000 in cash.

In 2001 Gilligan was sentenced to 28 years in prison for possession of commercial quantities of cannabis resin, a sentence later reduced to 20 years on appeal.

Veronica was carrying out investigative reporting on Gilligan's involvement in the illegal drugs trade.

After she was murdered, gardai had at one point more than 100 officers working on the case, which led to 214 arrests, 39 convictions, and 100 confiscations of guns, as well as confiscations of drugs and property worth millions.

In 2002 the Special Criminal Court issued an order for the confiscation and sale of Gilligan's 77-acre equestrian ranch at Jessbrook, Enfield, Co Meath.

From prison he contested this order in the High Court and won, on the grounds that the Special Criminal Court did not have jurisdiction.

This was later appealed in the Supreme Court and on December 21, 2005 the appeal was rejected unanimously. However, Gilligan's assets remained frozen by the CAB.

In January the following year the High Court cleared the way for the CAB to proceed with an application to have the equestrian centre and other property belonging to the Gilligan family handed over to the State.

Two years later, making a court appearance in an attempt to stop the State from selling off his assets, Gilligan accused his associate, John Traynor of having ordered the murder of Veronica.

In November 2012 the courts cleared the final barriers allowing the CAB to sell off the equestrian centre and Gilligan's house in Lucan.

The CAB is also continuing to pursue additional properties in Blanchardstown, West Dublin, and in Lucan.